One of the more confusing aspects of sous vide is whether or not to use an ice bath. There are times that using one is very important, times that it can be useful for flavor development, and times it isn't needed at all.
Because of this, people can take ice bath usage out of context and use it when they don't need to. Here is a detailed look at when you should use an ice bath, and when it doesn't matter.
When You Need a Post-Sous Vide Ice Bath
The only time you really need to use an ice bath is when you are going to store food for later and it has come right out of the sous vide machine. For example, you cook 5 bags of chicken breasts, eat one for dinner and put the others into your freezer, in the sous vide bags, to eat later.